Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $185.48   4.608%   $194.0269   $194.03   $194.05   $194.00  
  Purchase #2 $188.93   11.172%   $210.0373   $210.04   $210.05   $210.00  
  Purchase #3 $95.57   6.560%   $101.8394   $101.84   $101.85   $101.80  
  Purchase #4 $153.50   8.474%   $166.5076   $166.51   $166.50   $166.50  
  Purchase #5 $160.30   10.421%   $177.0049   $177.00   $177.00   $177.00  
  Purchase #6 $139.69   4.871%   $146.4943   $146.49   $146.50   $146.50  
  Purchase #7 $30.90   12.847%   $34.8697   $34.87   $34.85   $34.90  
  7 purchase totals = $954.37       $1,030.7801   $1,030.78   $1,030.80   $1,030.70